1. Technical Field
The present invention relates to an antenna device receiving an SDARS signal sent from an SDARS satellite, and more particularly, to an antenna element and an antenna module used for the antenna device.
2. Related Art
Recently, as known in the technical field, various antennas are mounted on vehicles such as an automobile. For example, an antenna for SDARS (Satellite Digital Audio Radio Service) is used as such an antenna.
The SDARS (Satellite Digital Audio Radio Service) is a digital broadcasting service using a satellite (hereinafter, referred to as “SDARS satellite”) in the United States. That is, in the United States, a digital radio receiver receiving a satellite wave or a terrestrial wave from the SDARS satellite to provide digital radio broadcasting has been developed and put in practical use. Currently, in the United States, two broadcasting stations of XM and Sirius have provided radio programs more than total 250 channels throughout the whole country. The digital radio receiver is generally mounted in a mobile object such as an automobile, receives the electric wave in the frequency band of about 2-3 GHz, and provides the radio broadcasting. That is, the digital radio receiver is a radio receiver capable of providing the mobile broadcasting. Since the frequency of the reception electric wave is about 2.3 GHz, the reception wavelength (resonance wavelength) λ at that time is about 128.3 mm. The terrestrial wave is formed in the manner that the satellite wave is received by an earth station, the frequency of the received satellite wave is slightly shifted, and the wave is re-sent in a linearly-polarized wave. That is, the satellite wave is a circular-polarized wave, but the terrestrial wave is the linearly-polarized wave.
The antenna device for XM satellite radio receives the circular-polarized electric wave from two geostationary satellites, and receives the electric wave by using terrestrial linear-polarized equipments in a blind zone. Meanwhile, the antenna device for Sirius satellite radio receives the circular-polarized electric wave from three orbiting satellites (synchro type), and receives the electric wave by the use of the terrestrial linear-polarized equipments in the blind zone.
Since the electric wave in the frequency band of about 2.3 GHz is used in such digital radio broadcasting, an antenna device receiving the electric wave is required to be installed outdoors. Accordingly, in order to mount the digital radio receiver in the mobile object such as the automobile, the antenna device is required to be mounted on the roof of the mobile object.
As the SDARS antenna, a planar antenna such as a patch antenna and a metal-plate loop antenna is used.
As the metal-plate loop antenna, there was well known a planar antenna in which distances from one another among an upper case, a planar antenna element, and a ground plate are kept and fixed accurately at predetermined distances (e.g., see Patent Document 1). The planar antenna disclosed in Patent Document 1 includes an upper case, a planar antenna element (metal-plate loop antenna) disposed on the back surface of the upper case at a predetermined distance, a ground plate disposed at a predetermined distance from the planar antenna element, an electrical conductor disposed between the planar antenna element and the ground plate, a circuit board attached to a lower surface of the ground plate, and electronic parts mounted on the circuit board. The electronic parts include a low noise amplifier (LNA). In the planar antenna element disclosed in Patent Document 1, there is a space between the planar antenna element and the ground plate, and an electromagnetic coupling type in which power is supplied to the planar antenna using the probe formed of the electrical conductor is employed.
Meanwhile, as the patch antenna, there was proposed “PATCH ANTENNA INCLUDING INTEGRAL PROBE” in which a conductive patch and a probe are physically coupled tightly (e.g., see Patent Document 2). In the patch antenna disclosed in Patent Document 2, a conductive patch includes an integral probe. The probe has a substantially rectangular shape and extends in a direction substantially perpendicular to the surface of the conductive patch. The probe is produced as a part of the conductive patch by using any available metal processing work in addition to punching, piercing, perforating, shearing, and shaping. In the exemplary embodiment, the probe is shaped by punching the conductive patch connected thereto. In order to perform the punching work, the probe is left as an integral part of the conductive patch connected thereto. In the patch antenna disclosed in Patent Document 2, the probe is shaped by punching the conductive patch so as to be bent from the center of the conductive patch toward the outside thereof. A dielectric spacer is provided between the conductive patch and a conductive substrate having a ground surface on a main surface, and the probe extends through the dielectric spacer. In Patent Document 2, the conductive patch is just mounted on the dielectric spacer, but the conductive patch is not fixed to the spacer.
A GPS receiving antenna suitable to be installed outside the vehicle is known (e.g., Patent Document 3). The antenna device disclosed in Patent Document 3 includes an antenna case formed by attaching a top cover and a bottom plate to each other, an antenna module which is housed in the top cover and receives a GPS signal, and a packing member which is disposed in the joint portion between the top cover and the bottom plate to seal the antenna module. The antenna module includes an antenna element for receiving a GPS signal sent from a GPS satellite, a circuit board on which a processing circuit for performing various signal processes such as amplification in signal for the GPS signal received by the antenna element is formed, and a shield case for shielding the processing circuit. The antenna element and the circuit board are attached to each other by a double-sided adhesive tape or the like.    Patent Document 1; JP-A-2001-24428    Patent Document 2: JP-A-7-106844    Patent Document 3: JP-A-2005-109687
In the above-described the metal-plate loop antenna disclosed in Patent Document 1, there is an air gap between the planar antenna element and the ground plate. For the reason, the metal-plate loop antenna disclosed in Patent Document 1 does not have an effect to shorten wavelength in case using a dielectric, thereby increasing size.
In the patch antenna disclosed in Patent Document 2, the probe is shaped by punching the conductive patch so that the probe is bent from the center of the conductive patch to the outside (toward the edge of the conductive patch) thereof. For the reason, the width between the bent portion (base of the probe) and the edge (side) of the conductive patch becomes smaller. As a result, when the probe is bent, the bent portion may be deformed. Further, in the patch antenna disclosed in Patent Document 2, since the conductive patch and the dielectric spacer are not fixed, there is a problem in that assembly is difficult.
In Patent Document 3, the antenna element is disclosed, but any detail configuration thereof is not disclosed.